JP2007051306A - Method for charging raw material into blast furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for charging a raw material into a blast furnace in an operation of controlling a coke ratio to a low value, which can keep a stable operation by securing the adequate reducibility of the whole ore layer, in particular, a fusion zone, while maintaining a high ratio of O/C. <P>SOLUTION: The method for charging the raw material into the blast furnace is a method of mixing at least one part of coke into an ore layer when alternately charging the coke and ore into the blast furnace so that they can form layers; and comprises predicting a distribution of the O/C which is a mass ratio of the ore to the coke charged into the blast furnace, in a radial direction of the furnace, and determining a mixing ratio of the coke into the ore at each radial position on the basis of the predicted ratio O/C. It is preferable to determine the mixing ratio M (mass%) of the coke to the ore at each radial position in the furnace, by using the predicted O/C and the following expression (a): M=X×(O/C-3.2)+M<SB>0</SB>, to mix the coke with the ore at the determined mixing ratio M (mass%) or higher, and to charge the mixture into the blast furnace. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a raw material charging method in a bell-less blast furnace when mixing at least a part of ore and coke and charging them from the top of the blast furnace.

Currently, the blast furnace operation in Japan is required to undergo major changes against the background of global environmental problems and iron ore and coking coal supply and demand problems. Low-reducing material ratio operation due to the need for CO ₂ reduction by the Kyoto Protocol, etc. that will come into force in 2005, and high-outcome ratio operation due to high production volume orientation will become mainstream. In the operation with a low reducible material ratio, a low coke ratio operation is required in which the coke ratio is reduced as much as possible while maintaining the pulverized coal blowing.

  However, when operating at a low coke ratio, the amount of carbon solution loss per unit mass of coke (sol loss) increases, the coke deteriorates due to an increase in coke residence time, and the pressure loss at the bottom of the furnace increases due to a decrease in the cohesive zone. Is known to be caused. When the accumulation of coke powder increases, the powder ratio of the furnace core increases, and the powder ratio increases particularly in the middle and near the center, leading to destabilization of the gas flow, causing fluctuations in wind pressure and unloading. Moreover, since the gas permeation force decreases due to a reduction in the gas unit consumption, it tends to have a peripheral flow tendency, heat loss increases, and shaft efficiency tends to deteriorate. Furthermore, the temperature rise of the charged raw material is delayed in the upper part of the furnace due to the increase in heat flow ratio, and it is easy to promote reduction stagnation and reduced powdering.

  In order to deal with these phenomena from the viewpoint of charging properties, it is effective to suppress coke deterioration and pulverization by increasing coke strength and reactivity, and to use raw materials with excellent reducibility. . In the blast furnace operation method in which sintered ore, pellets, lump ore, ordinary metallurgical coke and high reactivity coke having a JIS reactivity of 30% or more and an average particle size of 25 mm or less are charged, By adjusting one or more of the use ratio, particle size, and JIS reactivity of the highly reactive coke according to the reducibility, the thermal storage zone temperature is controlled to the optimum value, and the reduction reaction is promoted. There is known a technique capable of stable operation under a high reaction efficiency and a low reducing material ratio (see, for example, Patent Document 1).

  On the other hand, in the low coke ratio operation, the mass ratio of ore and coke increases, and the amount of coke charged to the blast furnace (hereinafter referred to as “coke base”) decreases relatively, resulting in a coke layer. The thickness decreases. Moreover, the diameter of the blast furnace shaft portion increases as it goes down, and the thickness of the coke layer further decreases as it descends in the furnace. When the coke layer thickness is below a certain value in a region called a cohesive zone described below, the gas flow is hindered and the operation is adversely affected.

  Therefore, if the coke base is increased, it is possible to avoid the coke layer thickness from decreasing below a certain value. In this case, the amount of ore charged into the blast furnace (hereinafter referred to as “or base”) is described. )) Also increases, and there is a concern that the temperature rise and reduction in the fused layer may be delayed. This is due to the following reason. That is, the ore charged in layers in the blast furnace rises in temperature while undergoing reduction as it descends in the furnace. Also, the load from above increases with the descent. Therefore, it is gradually deformed while filling the gaps between the ores, and becomes a fusion layer having a very high ventilation resistance below the shaft portion of the blast furnace. Since the gas flow resistance is large in the fusion layer, the gas hardly flows, and the gas mainly flows through the coke layer sandwiching the fusion layer. It is considered that the heat transfer to the fusion layer is dominated by the conduction heat from the gas flowing in this coke layer, and as the thickness of the ore layer (fusion layer) increases, the heat transfer and reduction at the center of the ore layer are inhibited. Is done. For the above reasons, maintaining the coke layer thickness by increasing the coke base is not always a solution.

  In order to solve the above-mentioned problems in low coke ratio operation, in an operation where the mass ratio of ore to coke (hereinafter referred to as “O / C”) is 4.5 or more, the in-furnace dimensionless radius is 0. A technique is known in which 5-40 mm small coke coke is mixed with an ore layer in the range of 5-1.0 and the mixing ratio is 1-10 mass% (see, for example, Patent Document 2). This is a technique aimed at forming a sharp gas flow at the center of the furnace in high O / C operation and suppressing local drooping of the cohesive zone from the middle to the periphery.

In addition, the sintered ore mixed with massive iron ore is charged as the lower layer on the previously charged coke layer, and only the sintered ore is charged as the upper layer on the upper part, On top of the charged coke layer, only the sintered ore is charged as the lower layer, and the sintered ore mixed with reduced iron is charged as the upper layer, and the sintered ore in the blast furnace ore layer is charged. Has been known to deposit so as to form two different layers (see, for example, Patent Document 3). This is because ore raw material with poor reducibility is charged into the lower layer, ensuring good reducibility of the entire ore layer and maintaining high O / C, reducing the reducing material ratio, and improving productivity. It is a technology that tries to perform stably.
JP-A-6-145730 JP 2002-003910 A JP 2002-327205 A

  However, the techniques described in Patent Document 2 and Patent Document 3 described above both control the cohesive zone at the time of low coke ratio operation in a macro manner. However, in the actual low coke ratio operation, the coke layer thickness is locally reduced, which inhibits the gas flow in the cohesive zone, leading to an increase in ventilation resistance and deterioration of unloading. In most cases, the prior art alone cannot address the problem of obstructing gas flow in the cohesive zone.

  Therefore, the object of the present invention is to solve such problems of the prior art and maintain a high O / C in the operation of a low coke ratio in a blast furnace, while maintaining a good cohesion zone in the entire ore layer. An object of the present invention is to provide a raw material charging method to a blast furnace that can ensure reducibility and thereby continue stable operation.

The features of the present invention for solving such problems are as follows.
(1) When charging coke and ore into layers in a blast furnace alternately, a method of charging at least a part of coke into the ore layer and charging the ore and coke charged into the blast furnace. The distribution in the furnace radial direction of O / C, which is the mass ratio, is predicted, and the mixing ratio of coke to ore at each radial position is determined based on the predicted O / C. Raw material charging method to blast furnace.
(2) Using the predicted O / C, the mixing ratio M (mass%) of coke to ore at each radial position in the furnace is determined by the following equation (a), and the mixing ratio M (mass%) The raw material charging method to the blast furnace as described in (1), wherein the coke is mixed with ore and the blast furnace is charged with the lower limit as the lower limit.
M = X × (O / C-3.2) + M ₀ (a)
However, X and M ₀ are constants that vary depending on the operating conditions, and X = 0.2 to 3.0.
(3) In a bell-less blast furnace equipped with a raw material charging device having a plurality of furnace top bunker and rotating chute, coke and ore are charged into different furnace top bunkers, and the opening degree of the discharge gate of each furnace top bunker The raw material charging method to the blast furnace according to (1) or (2), wherein the coke is mixed with the ore so as to obtain a predetermined mixing ratio by adjusting the blast furnace and charged into the blast furnace.

According to the present invention, it becomes possible to maintain good blast furnace air permeability even at low coke ratio operation, and the operation is also stabilized. For this reason, it is possible to reduce the amount of CO ₂ generated and contribute to the global environment.

  By mixing coke in the raw ore charged into the blast furnace (hereinafter referred to as “coke mixing charge”), the mixed coke plays the role of a spacer and suppresses softening deformation of the ore layer, Further, it is known that there is an effect of improving the air permeability of the fusion layer by securing the voids. The present inventors have examined in detail whether or not it is possible to compensate for the deterioration in air permeability due to the reduction in the thickness of the coke layer at the time of operation at a low coke ratio by using this coke mixed charging.

  Using the apparatus shown in FIG. 1, the change in the ventilation resistance was investigated by simulating the reduction of the raw material in the blast furnace and the temperature raising process. In FIG. 1, the raw material 2 charged in the graphite crucible 1 is loaded with a load from the upper part via a punch bar 4 by a load loading device 3 so as to be in the same level as the fusion layer at the lower part of the blast furnace. Heat with heater 5. 6 is a furnace core tube, and 7 is a thermocouple for controlling the heating temperature. The gas adjusted by the gas mixing device 8 is sent from the lower part of the crucible 1, and the gas that has passed through the raw material 2 in the crucible 1 is analyzed by the analyzer 9. A drop sampling apparatus 10 is installed at the lower part of the crucible 1. As the raw ore, a mixture of 50 to 100% by mass of sintered ore and 0 to 50% by mass of lump iron ore was used. FIG. 2 is an example of the experimental results, and is a graph showing the relationship between the ventilation resistance and the heating temperature when the amount of coke mixed with the ore is changed. When coke is not mixed, the ventilation resistance increases rapidly at a high temperature range of 1450 ° C. or higher, whereas when coke is mixed, the ventilation resistance decreases remarkably, and when the mixing amount is increased. It turns out that the effect becomes large. This is because the mixing of coke suppresses the deformation of the ore and maintains the voids in the vicinity of the mixed coke, preventing the phenomenon of increased airflow resistance due to the decrease of voids between particles due to the deformation of the ore. It was because it was done.

  Using this experimental result, the ratio of the ore and coke was kept constant, and the change in the airflow resistance of the fused layer when a part of the coke was mixed with the ore raw material was estimated by the calculation formula. The airflow resistance of the coke layer was given by Ergun's equation, and the airflow resistance of the fusion layer was predicted by Sugiyama et al. The experimental result measured using the apparatus of FIG. 1 was used as the contraction rate of the ore.

  In general, when the coke ratio is lowered without mixing coke, the airflow resistance increases due to the reduction of the coke layer thickness. On the other hand, FIG. 3 shows the calculation result of the cohesive zone ventilation resistance when the coke ratio is a constant value and a predetermined amount thereof is mixed with the ore layer. When the coke layer thickness is reduced at a constant coke ratio by mixing the coke with the ore layer, the air flow resistance of the softened layer is decreased by mixing the coke and passes through the cohesive zone as shown in FIG. Since part of the gas passes through the ore softening layer, the overall ventilation resistance is reduced. The ventilation resistance of the entire cohesive zone decreases with the mixing amount.

  The present inventors further proceeded with this study, and when the mass ratio (O / C) of ore and coke increases by 1, if 0.2 to 3.0% of coke is mixed with the mass of the raw material, It has been found that it is possible to prevent an increase in the ventilation resistance of the dressing. This is the result of the pressure loss value accompanying the increase in O / C from the experiment and the porosity of the fusion layer obtained in the load softening experiment when the mixing ratio of the coke to the ore is changed. It was obtained from a comparison with the pressure loss value of the cohesive zone calculated based on the change. The reason why the mixing ratio of coke to ore has a range is due to fluctuations depending on raw materials used, properties of coke (strength, particle size, etc.) or operating conditions.

  Accordingly, the distribution of the mass ratio (O / C) of ore and coke charged in the blast furnace in the radial direction in the furnace is predicted, and the coke for the ore is calculated based on the O / C at each position in the blast furnace. If the raw material is charged with a controlled mixing amount, the air permeability of the cohesive zone is ensured, and the reduction of the air resistance in the local area in the blast furnace is prevented, and it is good even in low coke ratio operation. It is possible to maintain a high blast furnace air permeability.

That is, the radial distribution of O / C after charging into the blast furnace is predicted, and the mixing ratio of coke to ore at each radial position is determined based on this result. By increasing the mixing ratio of coke at a position where O / C is large, a decrease in ventilation resistance is prevented. The mixing ratio of coke to ore is defined as M (mass%), and coke of M (mass%) or more given by the following formula (a) is mixed with the ore at the radial position to increase the permeability of the cohesive zone. It is preferable to ensure. In the formula (a), X and M ₀ are constants that vary depending on the operating conditions. Although M ₀ is normally set to 0 (zero), it can be determined empirically depending on the base blast furnace dimensions and operating conditions. In that case, a value of about 3 to 5 mass% is set. . X is suitably 0.2 to 3.0 mass% as described above. Mixing coke with M (mass%) or more into ore is effective in ensuring air permeability. However, the greater the amount of coke mixed, the better the air permeability, so the entire amount of coke is partially mixed into the ore. It is also possible to do.
M = X × (O / C-3.2) + M ₀ (a)
In order to predict the radial distribution of O / C after charging, for example, a calculation method using a mathematical model described in the literature (Sawada et al., Iron and Steel, No. 78, 1992, page 1337) There are also methods such as obtaining by an experiment using a cold model.

  In order to control the coke mixing amount at a predetermined radial position in this way, in a bellless type raw material charging apparatus having a plurality of furnace top bunkers, ore and coke are separately supplied to different furnace top bunkers. When storing ore and charging the ore into the blast furnace, a method of discharging coke from the bunker at the same time can be used. When using a raw material charging device with multiple furnace top bunkers, it is possible to control changes over time in the coke mixing ratio in the discharged raw materials by adjusting the opening of the discharge gate of each furnace top bunker It is. FIG. 4 shows a schematic cross-sectional view of the top of a bell-less blast furnace provided with a raw material charging apparatus having a plurality of top bunker. An embodiment of a method for controlling the coke mixing amount in the radial position will be described with reference to FIG. FIG. 4 shows a case where three furnace top bunker are provided. Ore is stored in the bunker 11, coke is stored in the bunker 12, the opening of the discharge gate 13 is adjusted, and the ore and coke are mixed. Charged into the blast furnace, a mixed layer 15 of ore and coke is formed in the blast furnace. The amount of coke mixed in the radial direction is controlled by adjusting the opening of the discharge gate 13 according to the tilt angle of the rotary chute corresponding to the raw material charging position. FIG. 4 shows a case where the coke layer 16 is formed only from the coke discharged from the bunker 12 and two ore and coke mixed layers 15 are formed. By preparing the next charging raw material in a bunker that is not in use, the raw material can be charged efficiently.

  For example, if the pattern of the tilt angle of the bellless chute is set to coke layer: 54, 54, 53.5, 53.5, 53, 53, 52.5, 52.5, 52, 52, 51, 51, 50.5, 50.5, 50, 49.5, 49, 48, 45.5, 42.5, 38.5, 26, 15 (°), ore layer (1): 50, 49, 48, 48, 46.5, 46.5, 45.5, 44.5, 43.5, 42.5, 41.5 (°), ore layer (2): 51, 50.5, 50, 50, 49, 49, 48 (°), the case where the coke layer 16, the ore layer (1) 15a, and the ore layer (2) 15b are charged as shown in FIG. FIG. 5 shows the result of predicting the O / C distribution in the radial direction of the furnace using model calculation. Based on the results shown in FIG. 5, the coke mixing ratio distribution in the radial direction is set as shown in FIG. 6, and the cut-out control of the furnace top bunker is performed, so that the coke is calculated based on the predicted O / C distribution. The present invention can be implemented by charging the mixed ore into the blast furnace.

  In the above example, the tilting direction of the rotary chute is changed from the blast furnace wall side to the center direction, but by controlling the rotation chute from the center to the furnace wall direction, the controllability of the raw material charging position can be further improved. In order to improve the controllability of the inner coke mixing ratio distribution, it is also preferable to set the rotation direction of the rotating chute from the center to the furnace wall direction.

In order to clarify the effect of the present invention, in the bell-less blast furnace having the raw material charging apparatus shown in FIG. The operation test of 1-7 was implemented. The blast furnace has an inner volume of 5153 m ³ , a furnace port diameter of 11.4 m, a hearth diameter of 15.0 m, and has 40 tuyere. The base operating conditions are a coke ratio of 400 kg / t-pig and a tapping amount of 11850-12300 t / d (No. 1). First, the coke ratio was reduced from the base conditions. At that time, the or base was kept constant and the coke base was lowered (No. 2, No. 3). On the other hand, the coke base was lowered while keeping the ore base constant, but at the same time, a part of the coke to be charged was cut out from a separate furnace top bunker at the time of ore charging and mixed. At this time, the O / C distribution of the raw material charged in the furnace was calculated and predicted in advance, and the coke mixing amount was calculated by the above equation (a) based on the predicted O / C distribution. The cut-out control of the furnace top bunker was performed so as to obtain a mixed amount, and the ore mixed with coke was charged into the blast furnace (No. 4 to No. 7). Table 1 shows the results of the operation test.

  No. which is a comparative example. 2, no. In No. 3, the airflow resistance increased as the coke ratio decreased, and adverse effects such as unstable load drop occurred, and the low coke ratio operation could not be continued. 4-No. In the operation experiment of No. 7, stable low coke ratio operation was possible, and the coke ratio could be reduced to 240 kg / t.

It is the schematic which shows the structure of the apparatus which measures the high temperature property of an ore. It is a graph which shows the change of the ventilation resistance in the high temperature of an ore layer and a coke mixed layer. It is a graph which shows the change of the air permeability of an ore fusion zone by coke mixing. The cross-sectional schematic of the furnace top part of the bell-less blast furnace which installed the raw material charging device which has a some furnace top bunker. It is a graph which shows the charge O / C radial direction distribution to a blast furnace. It is a graph which shows the coke mixing ratio radial direction distribution targeted with respect to O / C distribution of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 2 Raw material 3 Load loading apparatus 4 Punch rod 5 Heater 6 Furnace core tube 7 Thermocouple 8 Gas mixing apparatus 9 Analyzer 10 Droplet sampling apparatus 11 Bunker 12 Bunker 13 Discharge gate 14 Rotating chute 15 Mixed layer of ore and coke 15a Ore layer (1)
15b Ore layer (2)
16 Coke layer

Claims (3)

  When charging coke and ore into layers in a blast furnace alternately, a method in which at least a part of coke is mixed and charged in the ore layer, the mass ratio of ore and coke charged in the blast furnace. The distribution of O / C in the furnace radial direction is predicted, and the mixing ratio of coke to ore at each radial position is determined based on the predicted O / C. Raw material charging method. Using the predicted O / C, the mixing ratio M (mass%) of coke to ore at each radial position in the furnace is determined by the following equation (a), and the mixing ratio M (mass%) is a lower limit value. The method for charging raw material into a blast furnace according to claim 1, wherein coke is mixed with ore and charged into the blast furnace.
M = X × (O / C-3.2) + M ₀ (a)
However, X and M ₀ are constants that vary depending on the operating conditions, and X = 0.2 to 3.0.   In a bell-less blast furnace equipped with a raw material charging device having multiple furnace top bunker and rotating chute, coke and ore are charged into different furnace top bunkers, and the opening of the discharge gate of each furnace top bunker is adjusted. The method for charging raw materials into a blast furnace according to claim 1 or 2, wherein coke is mixed with ore so as to obtain a predetermined mixing ratio.

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